1. Field of the Invention
The present invention relates to a reinforcing bar binding machine including a binding device which binds arranged reinforcing bars by twisting a wire looped and wound around the reinforcing bars.
2. Background Art
In a reinforcing bar arrangement process of a reinforced concrete construction work, as a tool for binding reinforcing bars at a crossing point, etc., of reinforcing bars, a reinforcing bar binding machine is known. This reinforcing bar binding machine is provided with a binding device for binding reinforcing bars. As shown in JP-B2-3496463, this binding device includes a sleeve which is provided inside the binding machine body and has reinforcing bar binding hooks pivotally mounted to the tip end, a tip end shaft which is fitted to the inside of the sleeve and generates a load for advancing and retreating and rotating the sleeve, and engaging means (fins) for controlling the rotation of the sleeve in cooperation with rotation stoppers provided on the binding machine body, and advances the sleeve by rotating the tip end shaft by a motor, and accordingly, closing and actuating the hooks to make the hooks grasp the reinforcing bar binding wire, and further rotates the hooks together with the sleeve to twist the wire and bind the reinforcing bars.
In the binding mechanism described above, the sleeve has a double structure including an outer sleeve and an inner sleeve, and the front portion of the outer sleeve holds the hooks rotatably and the rear portion of the outer sleeve prevents the key engaging with a screw groove of the tip end shaft from coming out, and to the front portion of the inner sleeve, a shaft for holding a guide pin for opening and closing the hooks is attached, and the rear portion holds the key in a fitting manner. The outer sleeve and the inner sleeve are actuated integrally, so that for integrating these sleeves, as shown in FIG. 11, a set screw 53 is screwed into the inner sleeve 52 from the outer sleeve 51.
However, according to the configuration described above, between the tip end shaft and the hooks which actually grasp and twist the wire, four components such as the tip end shaft 54, the key 55, the inner sleeve 52, the set screw 53, the outer sleeve 51, and the hooks 56 are interposed, and this makes the structure complicated.
A load is transmitted from the inner sleeve to the outer sleeve via the set screw 53, however, downsizing takes precedence, so that a large-sized fixing tool cannot be used, and the set screw 53 easily loosens during repeated use.
A pair of hooks 56 (one is not shown) are attached to the front end of the outer sleeve 51, and the rear portion of the outer sleeve covers the key 55 and prevents it from coming out toward the outer periphery, so that the outer sleeve is inevitably formed to be long in the front-rear direction outside the inner sleeve 52, and this double structure cannot be avoided, so that the diameter inevitably becomes large and the weight is also heavy.
In addition, a compression spring 57 is installed between the inner sleeve 52 and the tip end shaft 54 so that the hooks 56 come to predetermined opening positions in an initial state, and between these components, resistance is generated to some degree so that the inner sleeve 52 easily rotates together with the tip end shaft 54, however, the compression spring 57 is disposed inside the inner sleeve, so that the spring load cannot be increased.
Further, in the wire twisting mechanism, the tip end shaft is fitted to the inside of the sleeve, and the rotation of the tip end shaft is converted to advancing and retreating and rotation of the sleeve, and in particular, when the sleeve retreats to a standby position after finishing a twisting operation, the two hooks must be positioned at predetermined angles, that is, at both sides of the wire at the advancing end of the sleeve. Therefore, in the latter half of retreating movement of the sleeve, one fin of the sleeve and rotation stoppers of the binding machine body are disengaged and the sleeve retreats while rotating, and when the other fin engages with the rotation stoppers and the hooks come to the predetermined angles, the standby state is obtained. In rotation after the disengagement, a spring collar and a compression spring are provided between a jutting part provided on the base portion of the tip end shaft and the sleeve, the spring collar is pressed against the sleeve by a compression load of the compression spring along with the retreating movement of the sleeve, and due to a frictional force between these, the tip end shaft and the sleeve are rotated together.
However, the sleeve is supported rotatably on a support member provided on the reinforcing bar binding machine main body and engaged with other members. Normally, between the sleeve and these members, grease is applied, so that the frictional force is maintained small, however, the grease becomes insufficient in some cases. In the operation environment of the reinforcing bar binding machine, fine debris and fugitive dust float, so that the grease may absorb fine debris and fugitive dust. In these cases, the lubricating function is deteriorated and the frictional force between the sleeve and the members increase, and a phenomenon easily occurs in which the sleeve cannot rotate together with the tip end shaft and the hooks cannot completely return to the standby positions. If the hooks cannot return to the standby positions, due to the incorrect orientations of the hooks, the wire cannot be grasped during the twisting operation, and a twisting failure may occur. To prevent this phenomenon, it is necessary to use a thick compression spring with a great spring load and increase the frictional force between the sleeve and the tip end shaft by adding components, and this makes the structure large in size and complicated, and results in a cost increase.